Test of light-lepton universality in $\tau$ decays with the Belle II experiment

Belle II Collaboration, I. Adachi, K. Adamczyk +428

We present a measurement of the ratio $R_{\mu }=\mathcal{B}({\tau }^{-}\to {\mu }^{-}{\bar{\nu }}_{\mu }{\nu }_{\tau })/\mathcal{B}({\tau }^{-}\to e^{-}{\bar{\nu }}_e{\nu }_{\tau })$ of branching fractions $\mathcal{B}$ of the $\tau$ lepton decaying t…